Confusion on Extension Tubes

[rick_tyrseck]

Have Canon's 17-40L, 24-105L & 70-200 f4L as my lens set up and I want to do

more macro/close-up photography.

 

In looking at the kenko set of 3 (12, 20 & 36mm), I am not sure if I understand

the exact focal benefits of these 3 different ext tubes. Very much a newbie

here and I didn't find any other thread on photo.net that helped explain what

the benefits are for each of the 3 sizes. i.e. if my 2 shorter lenses all

generally haver an 18+ inch close focusing limit, what do these tubes allow me

to do. Thx....Rick

[sattler123]

The tubes allow you to get closer to your subject and thereby increasing the size you can capture.

[nathan_meador]

they allow you to get closer to the subject, sorta like a macro lens, giving slightly better magnification. You could probably do a search under 'extension tube' to find more.

[jon_worth]

I do not actually own any extension tubes (yet), but one thing to consider is that the cheapo-brand ones will not permit autofocus because they lack the electrical contacts to connect the AF system of the camera to the lens.

 

This may or may not be a problem depending on how confident you are in manual focusing, how good your eyesight is, and/or how good (i.e. big/bright) your camera's viewfinder is.

[JeffOwen]

Make sure you get the extension tubes WITH the electrical through connections.

 

Note that extensions tubes will give you fantastic close up opportunities but beware that quality of the images may not be as good as from a designed Macro lens. This is because complex lenses (especially zooms) work within very tight focus ranges and if you move them out of that range then you may be disappointed. I have a set and love them.

[jcolwell]

Here's some good reading on macro photography.

 

<p><a href="http://www.photo.net/learn/macro/primer">Macro Photography by Philip Greenspun</a>

<br><a href="http://www.earthboundlight.com/phototips/closeup-choices.html">Earthbound Light</a> photo tips.

<br><a href="http://www.photostuff.co.uk/closeup.htm">© Bob Manekshaw Close-Up Photography</a>

calcs

<br><a href="http://www.imaginatorium.org/stuff/cufilter.htm">Cognointellectual Optics </a>

<br><a href="http://xoomer.alice.it/ripolini/Close_up.pdf">closeup calculators</a>

[rick_tyrseck]

Okay...thanks.....if I go with a Canon ET, do people have a preference of the 12mm vs the 25mm? .....and why?

[geoff_foale]

It depends on exactly what you want to do, but you probably will get most benefit with the 70-200 as the other lenses already close focus, as you said.

 

I haven't used the Kenko tubes but use a Canon tube on my Canon 70-300 (no real benefit on smaller lenses like my 28-135). Not as good as a proper macro lens but if you just want bigger close up shots, ie insects where you are looking at a focusing distance around 3 to 4 ft. it will help. Even with proper Canon equipment they recommend manual focus, although autofocus will work with Canon tubes. I agree, when using autofocus I was disappointed with the results but get sharp results with manual focusing upto around 20 ft.

[alan_myers]

The Kenko tube set that costs roughly $160 US is fully auto focus compatible and works fine. I have and use it, along with two Canon 12mm and one Canon 25mm tubes.

 

I think you will find them most useful on your 70-200.

 

The reason that there are 3 different sizes is to work with various

lens focal lengths and to make for a total of seven possible lengths of extension, between all the possible combinations of tubes.

 

I recommend you use only a single tube, when possible. Using more does tend to slow down AF a little bit (due to light fall off and the electronic communication between camera and lens needing to cross more joints).

 

By the way, the loss of AF when shooting macro isn't really all that big a deal. I often just turn it off, even on dedicated macro lenses. It's more convenient to simply move yourself, the camera and the lens closer to or further from the subject until focus is achieved.

 

But, the real issue is that the cheap tubes without electronic contacts not only stop AF from working, the electronically controlled lens aperture also will only function at it's largest setting because there are no signals transmitted from the camera telling it to stop down. (There might be a workaround, a way of mounting the lens on the camera first, using depth of field preview to stop the lens down, then remounting it onto the extension tube. But, I've never tried this, don't have any of the cheap tubes myself, and it sounds like a pain in the arse even if it does work.)

 

The amount of extension you need varies depending upon lens focal length. For example, I've used a 12mm behind a 20mm Canon lens. The subject was a flower, and it's petals when in focus were actually touching the front element of the lens!

 

Rule of thumb, for 1:1 or lifesize magnification you need approx. the same amount of extension as the lens' focal length. Based on this, 50mm of extension would be needed behind a 50mm lens.

 

However, this is just a rough estimate and not entirely true with all lenses, because all lenses' inherent close focusing capabilities vary, among some other factors. So, just give it a try, you'll quite easily be able to see how much magnification you are getting through the viewfinder.

 

I first learned about using extension tubes roughly 25 years ago, and a set has been in my camera bag with each and every camera system I've used, ever since. They are super handy for macro, near macro and just simple closer focus with long lenses.

 

FYI, eventually you might come across a "macro bellows" or "macro helicoid" (both of which are also sometimes called other names).

 

These are also extension tubes, of a sort. Both of them are adjustable, though, unlike the rigid tubes you are considering. Bellows, in particular, give continuous variation over a very wide range of magnifications. Helicoid also give continuous variation, but in a more limited range.

 

There are some third party bellows available for EOS cameras and EF lenses, but I'm not aware of any helicoids made to fit them.

 

The problem with bellows is that they are large and somewhat fragile, so more difficult to work with out in the field. However, they can offer much more extension and thus much higher magnification than tube sets.

 

Canon offers the MP-E 65mm Macro lens, which sort of takes the place of a macro bellows. It has a magnification range of 1:1 (life size) to 5:1 (five times life size), which is similar to some typical bellows/lens combos.

 

Extension tubes are a great way to experiment with macro relatively inexpensively. Using them can help you decide if you like shooting macro, and just how much magnification you really need. Many people think they want really high magnification, but actually end up shooting not much more magnification than 1:2 to 2:1, or the visible range from about half life size to twice life size. Much more magnification than that is getting into an "normally unseen world" and almost a different type of macro photography.

 

Have fun!

[chrisjb]

I use olympus OM and hasselb;ad tubes, manual focus just movin the camera handheld, but stopped down to gain DOF is harderm there is little in macro, the farther the lens from the sensor the greater magnification and less DOF, also I think single FL easier to work with like the 50 f1.8. Bellows are cheaper these days lke m42, I use an FD auto bellow and keep a 50 1.4 and 100 2.8 for it. here is FD bellows + FD100 2.8 on Dslr:)<div></div>

[jon_worth]

Alan -- Excellent point about the loss of aperture control when using "dumb" extension tubes. Very informative post, thanks! :-)

 

--Jon

[chrisjb]

BTW, if you notice the FD auto bellows has a cable release. this allows focussing wide open, then the cable release used to close the aperture down just before shooting. a little easier than being stopped down with manual tubes :)

[chrisjb]

Or some M42 bellows ...